1. Field of the Invention
The present invention relates to a character display control circuit which controls display of characters on a screen.
2. Description of the Related Art
Heretofore, a television receiver and a video tape recorder (VTR) which have on-screen functions of displaying character data of every kind on a television screen according to instructions of viewers have been known. Such an on-screen function is generally achieved by a microcomputer having a video RAM (VRAM) and a character ROM. More specifically, a character code corresponding to a character to be displayed is stored in an address of the VRAM corresponding to the portion of a television screen on which the character is displayed. According to horizontal or vertical scanning of television signals, the character code is then read out of the VRAM. On the other hand, a dot pattern of character font for each of all the characters which can be displayed on the television screen is stored in the character ROM. Thus, the character is displayed on the television screen according to the character code read out of the VRAM and the dot pattern of character font read out of the character ROM.
Here, a device with such an on-screen function also has a function of changing the size of a character to be displayed. This size change is executed by changing the frequency of a display clock of the character and controlling a period of displaying one dot. For example, if the frequency is reduced to two thirds, the display period will become one and a half times, whereby the size of character in a horizontal direction can be one and a half times.
However, such a device has a disadvantage that the start position of a horizontal display position of the character gets out of position. In other words, the display start position is determined according to count of the display clock. When the frequency of the display clock is changed, even though the same counted value has been set, the display start point differs. Thus, the display start position gets out of position.